Thermal relay for fluorescent lamps



Aug. 10, 1943. H. J. M CARTHY THERMAL RELAY FOR FLUORESCENT LAMPS FiledSept. 12, 1940 J j'l' aa'rlizy INVENTOR.

ATToE/ve Y through the eyelets 4. The resistance Patented Aug. 10, 1943UNITED STATES PATE NT OFFICE THERMAL RELAY FOR FLUORESCENT LAMPS HenryJ. McCarthy, Danvers, Mass, assignor to Sylvania Electric Products ofMassachusetts Inc., a corporation Application September 12, 1940, SerialNo. 356,566

1 Claim.

lamp to be preheated before the discharge is I started between them.

Another object is to provide a starting switch which will be so timed inits action that no greater interval of time will elapse for thepreheating of the cathode than is absolutely necessary.

A further object is to provide a switch which will function under allstarting and restarting.

Another object is to provide a switch which will be so mounted as to becapable of withstanding accidental, careless or rough usage withouthavpossible conditions of ing the precisely adjusted parts thrown out ofalignment.

A feature-of this starting apparatus is that it eliminates theunnecessary time lag present in many switches during the starting andrestarting period. I

Another feature of this switch isthat it is so mounted that even if itwere dropped or otherwise mishandled, the precisely adjusted parts wouldnot be disturbed.

Other objects, advantages and features will be apparent from thefollowing specification taken in conjunction with the accompanyingdrawing in which:

Figure 1 is a front perspective of the thermal relay assembly with themounting plate shown dotted for clarity.

Figure 2 is a side elevation detail of the thermal relay.

Figure 3 is a front perspective viewed from below of the thermal relayassembly with the container partly cut away tov show the insulatingmeans.

Figure 4 is a schematic wiring diagram of the thermal relay.

Similar reference characters refer to similar parts in the several viewsof the drawing and in the specification which follows. The switch in myinvention comprises a condenser, a resistance rod supported between andconnected to the two lead-in wires, a bimetallic strip bent around theresistance rod, and a high and two low resistance points.

The condenser I is mounted on the mounting plate 2, having its lead-inwires 3 rod 6, supextending ported between and connected to the lead-inwires I and 8, is also mounted on the mounting plate 2 but on the sideopposite the condenser I. The lead-in wires 1 and 8 of the resistancerod 6 are joined to the lead-in wires 3 of the condenser at the eyelets4. The joining of these two sets of lead-in wires at the eyelets 4 maybe done by spot-welding, soldering or some similar means.

The lead-in wires 3 of the condenser I are projected through the eyelets4 in the mounting plate 2. and extend down through the eyelets 9 in thecircular base plate III and into the base pins 5 where "they may besoldered. Although eyelets 4 and 9 are used in the mounting plate 2 andthe base plate I0, respectively, any other material may be used thatwill permit a joining and fixing of the lead-in wires at these points.Eyelets, or some similar means are necessary due'to the fact that thebase plate and mounting plate are made of Bakelite or some similarinsulating material.

The supporting arm II of nickel or some similar material extendsinwardly from the lead-in wire I, and attached to the inward end thereofis the bimetallic strip I2 which is bent around the resistance rod 6.Attached to the inner side of the free end of the bimetallic strip I2 isthe low resistance contact 25. The resistance rod may have thereon aninsulating coating I3 of, for example, alumina and shellac.

I have found that an insulating coating of alumina and shellac is bestsuited for the particular purpose for which it is herein employed. Iapply two coats of a dewaxed shellac and then two coats of analumina-shellac mixture. Each coat isbaked before another coat isapplied. Although I have used two coats of shellac and twocoats ofalumina and shellac the number of coats may be varied inasmuch asuniformity of the -coating is the object to be attained. I have justapplied two coats of shellac before applying any alumina because withthe shellac foundation a higher breakdown voltage is obtained. Thiscoating also prevents the bimetallic strip from cutting through theresistance rod.

wardly therefrom and The supporting arm I4 of nickel'or some similarmaterial extends inwardly from the lead-in wire 8 and attached theretoand projecting upparallel to the bimetallic strip I2 is the strip I5 towhich is attached the U-shaped arm I6 of nickel or some similarmaterial. Attached to one end of this U-shaped arm is the highresistance contact II, which maybe of carbon and which is normallyclosed with the bimetallic strip I2. Attached to the other end of theU-shaped arm is the low resistance contact I8, which may be of silverand which is normally open in respect to the bimetallic strip 12. Thislow resistance contact acts as an auxiliary starting means for if thefilaments of the lamp have not been sufliciently heated to start thedischarge across the lamp by the time the bimetallic strip breaks awayfrom the high resistance contact H, the voltage across the resistancerod 6 will continue to heat the bimetallic strip l2 and cause the stripl2 to bend back causing the low resistance contact 25 attached thereto,to touch the low resistance contact l8 thus short-circuiting theresistance rod and starting the preheating of the lamp filaments.

The resistance rod should have a high resistance, say 40,000 ohms. Forthis resistance I have used, for example, a resistance rod, 0.45 inchlong and .065 inch in diameter. For my high resistance contact I haveused carbon, having a contact resistance of about 15 to 30 ohms. For mylow'resistance contacts I have used silver, having a resistance of afractional part of an ohm. Although I have used these particularmaterials, my invention does not necessitate the use of these exact samematerials. It is suiiicient that a high resistance contact point, lowresistance contact points andahigh resistance rod be used. A condenserof .006 microfarad across the contacts has proven to be advantageous forthe elimination of radio interference.

The mounting plate 2 is not mounted flush on the base plate [0, but isso out as to be elevated from the base plate at the points where thecondenser lead-in wires 3 extend down into the If this were not done itwould be cuite difficult to centrally locate the mounting base pins 5.

plate 2 on the base plate l and still have the wires 3 extending downinto the base pins in their proper positions. The base pins may be ofthe type suitable for use in a socket of the type described in thecopendingapplication, Serial No. 331,793 filed April 26, 1940.

The manner in which this switch is mounted allows for considerableaccidental misuse. Due to the fact that several of the partswhich' arevital to the operation of the switch are very finely proportioned andthe slightest change therein would cause ineffective or inefiicientoperation, this switch is mounted in a manner as to have those partswhich are not finely proportioned and sensitive, absorb the shocks ofaccidental misuse.

The lead-in Wires 3 of the condenser I are quite flexible. Due to thisflexibility of these wires, and the fact that the mounting plate 2 isnot flush mounted on the base plate l0, any movement or disturbance ofthe base plate will not disturb the switch elements because the switchmount as a unit will merely bend forward or backward, the shock'beingentirely absorbed by the flexible lead-in wires of the condenser.

The entire switch unit may be inserted in a metal container I9 and maybe insulated therefrom by a thin tube of insulating paper 22 around theinner wall of the container l9. and a wafer 21 of insulating material inthe top of the container. -Ihis container may have several tangs 20, onthe open end which may bendg over the base 'plate l0 after the switchhas been inserted in the container. The base plate ID has severalnotches 2|, therein, over which the tangs 20 are bent. If these tangs 20ever became loose and permitted the base plate to move, the switch wouldnot be afiected, for the movement of the switch would be absorbed by theflexible wires 3 of the condenser, thereby protecting the more sensitiveand vital parts of the switch and preventing them from being thrown outof alignment.

The contour of the mounting plate may take any desired shape. Thecontour, as shown in Figure 1, has been selected because it facilitatesand makes easier the welding operations on the thermal relay. Thecontour of the sides of the base pins may be fiat or grooved dependingon the type of contacts used. If a wire contact is used, I have foundthat pins with grooved sides provide a firmer contact surface.

What I claim is:

In a thermal relay for electric gaseous discharge lamps: a pair of rigidlead-in wires; a relay means attached to said lead-in wires, said relaymeans comprising: a resistor, a'contact of material such as carbonhaving a high contact resistance, a low resistance contact, a bimetallicstrip electrically contacting said high resistance contact when saidresistor is unenergized and in a position to be distorted by the heatdeveloped in said high resistance contact when the latter passescurrent, and to open said contact when distorted sumciently, saidbimetallic strip also being so positioned as to be distorted by the heatdeveloped in said resistor when the latter passes current and to shortcircuit said resistor bymaking contact with the low resistance contact,when distorted sufficiently; amounting plate of insulating material onwhich said relay means is mounted through said lead-in wires, acondenser mounted through semi-flexible lead-in wires on said mountingplate on the side opposite the relay means, a base plate of insulatingmaterial to which saidmounting plate issubstantiallyperpendicular,a-pair of contact pins extending fromsaid base plate, said lead-in wiresof said condenser extending through said mounting plate and base plateand into said base pins, 2. metal container enclosing said thermal relayand attached to said baseplate and a tube of insulating paper woundaround the inner walls of said container to insulate said'container fromsaid thermal relay.

HENRY J. MCCARTHY.

